In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
As the wavelength of the exposure source have been shortened, resist materials for use with these types of exposure light sources required improvement in lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base component that exhibits a changed solubility in an alkali developing solution under action of acid and an acid generator that generates acid upon exposure.
Conventionally, as the base component for these chemically amplified resists, resins have been mainly used. For example, polyhydroxystyrene (PHS) or derivative resins thereof in which the hydroxyl groups are protected with acid dissociable, dissolution inhibiting groups (PHS-based resins), a copolymer derived from (meth)acrylate ester and a resin in which a part of the carboxy groups within such a copolymer are protected with acid dissociable, dissolution inhibiting groups, and the like have been used.
Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
As acid generators usable in a chemically amplified resist, various types have been proposed including, for example, onium salt-based acid generators such as iodonium salts and sulfonium salts (see for example, Patent Document 1).                [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385        